View full sizeMolly Harbarger/The OregonianThis single white oak in Kronberg Park is fenced off to keep people from getting too close after an arborist told the city the tree could fall at any moment. The arborist's opinion was solicited during a debate whether the tree should be saved from TriMet destruction.

The Milwaukie City Council gave TriMet the go-ahead to start construction on Kellogg Bridge in Kronberg Park. Construction is slated to begin in earnest in summer, but a temporary permit allows TriMet to prepare the site now so construction stays on TriMet’s schedule.

TriMet and Milwaukie are still negotiating how much TriMet owes Milwaukie for building in the park, so TriMet must return to council to ask for the final approval later.

The bridge application came under fire in January when City Council took up the complaints of two residents and appealed the Planning Commissions’ approval of TriMet’s construction plan over a single white oak tree residents wanted to save.

Arborist Terrence Flanagan said the tree is healthy, and while it could cost TriMet more money, could be preserved during construction.

Leah Robbins, TriMet’s east segment director, agreed to a late insertion of language that requires TriMet to follow the arborist’s suggestions to protect the tree. She said TriMet received the report this afternoon, so hasn’t fully reviewed it.

“But the construction effort will include all those tree protection efforts,” Robbins said.

The 7.3-mile Orange Line between Portland and Oak Grove is slated to open in September 2015. Construction began in June on the centerpiece of the project, a 1,720-foot bridge over the Willamette River, and designs are 90 percent complete for the rest of the line. Construction of the segment extending east from the river could begin as early as February.